This invention relates to a permanently magnetized rotor which, upon rotation, produces a zone of high-density, rapidly reversing flux through which pieces of different metals may be passed for magnetically separating them into groups. This rotor relates to the method and apparatus for sorting non-ferrous metal pieces disclosed in our U.S. Pat. Application Ser. No. 07/093,197, filed Sept. 4, 1987, now U.S. Pat. No. 5,834,870.
It is conventional to shred or break scrap automotive vehicles into small pieces. These pieces comprise different metals which are mixed together as a result of the shredding or breaking operation. Magnetizable ferrous metal pieces may be removed by suitable magnetic devices. This leaves a residue of pieces formed of different metals, such as of lead, zinc, copper, brass, aluminum and stainless steel, which do not respond to magnetic removal devices. These pieces of metal are worthless when mixed together, but can recycled and reused if they are separated into groups of like metals.
In the past, the separation or sortation of the non-ferrous metal pieces (including stainless steel as a non-ferrous metal because of its lack of response to magnetic sorting devices) has been done manually. That is, a worker visually observes a collection of commingled pieces and visually selects, and manually removes from the collection, those pieces which appear to be of the same metals. Particularly when dealing with automotive scrap metal, the different metal pieces can be readily observed because of their different shapes or appearances. However, this requires a considerable amount of labor and is a slow method of sortation. As a practical matter, this can be accomplished only in places where the labor costs are exceedingly low, such as in some of the Third World countries. Thus, in the past, shipments of mixed pieces of scrap metal have been sent to such countries by ship and, after the metal pieces have been sorted, they have been returned for re-melting and re-use. Because of the considerable shipping expense, notwithstanding the low labor costs, it has been not feasible, in many instances, to sort such mixtures of different metal pieces and, therefore, these have merely been discarded without further use.
We have discovered that subjecting such non-ferrous metal pieces to a high-density, rapidly changing, strong magnetic flux field induces an eddy current in the pieces which produces a repulsive magnetic force in the pieces that is generally proportional to the types of metal which the pieces comprise. This repulsive force can cause the respective pieces, when passed through a zone of such flux, to freely travel away from the field in different length trajectories, depending upon the types of metal. Thus, by subjecting substantially similar-size pieces to such a magnetic flux field, their different trajectories permit collecting the pieces in groups of different metals.
By way of example, when moving different pieces, of approximately the same size, of different metals through a zone or area of such rapidly changing, high-density, strong magnetic flux field, the pieces made of aluminum tend to freely fly a much greater distance from the field than pieces of copper, which in turn fly further from the field than pieces of zinc. Brass pieces remain closer to the field and lead pieces remain even closer. Hence, different material pieces are magnetically sorted into like metal groups by the distance which they travel.
In order to produce the required magnetic field, a magnetic rotor may be utilized. This invention relates to a permanent magnet rotor which produces a very high flux density, rapidly changing, strong flux field in a preselected zone through which scrap metal pieces may be passed for sortation purposes. However, this rotor may also be utilizable for other purposes where a similar magnetic field is desirable.